No door ever closed but another one opened
Cha do dhùin doras nach do dh'fhosgail doras
Here are two more Gaelic idioms which feature nach :
Am fear air nach tàinig, thig
He who has not yet tasted misfortune, will [lit. The man on whom it hasn't come, it will come]
Cha do smaoinich nach do rinn
Thoughts are the seeds of deeds [lit. Not thought, not done